Method and System for Controlling Emission from an Off-Road Engine

ABSTRACT

In a method and system for controlling emission from a four-stroke off-road engine that is provided with an exhaust gas discharging assembly at a downstream side thereof for discharging of the exhaust gas from the off-road engine, the exhaust gas discharging assembly is provided with an oxidation catalyst for converting hydrocarbon and carbon monoxide, and the method includes the steps of injecting a fuel rich fuel-and-air mixture into the off-road engine, and injecting fresh air into the exhaust gas discharging assembly at an upstream side of the oxidation catalyst.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method and an emission control system forcontrolling emission from an off-road engine, more particularly to amethod and an emission control system involving injecting a fuel richfuel-and-air mixture into an off-road engine and fresh air into anexhaust gas discharging assembly for controlling emission from theoff-road engine.

2. Description of the Related Art

In order to meet emission standards, such as CARB III and EPA III, whichwill be applicable to many states of the United States in the nearfuture, conventional gasoline off-road engines, particularly forfour-stroke engines with a power output of less than 30KW, normallyincorporate electronic fuel injection (EFI) means therein for adjustingan optimum air/fuel ratio of a fuel-and-air mixture to be injected intothe off-road engine. However, this approach is relatively expensive andis not economically suitable for application to the off-road engine witha carburetor. In addition, conventional off-road engines normallyproduce a high concentration of NO, in the exhaust gas and thus requireinstallation of a reduction catalyst (Rh), which is used to reduce NO,in the exhaust gas, in addition to an oxidation catalyst (Pt/Pd), whichis used for converting hydrocarbon and carbon monoxide in the exhaustgas into water and carbon dioxide.

SUMMARY OF THE INVENTION

Therefore, the object of the present invention is to provide a methodand an emission control system that can overcome the aforesaid drawbacksof the prior art.

According to one aspect this invention, there is provided a method forcontrolling emission from an off-road engine. The off-road engine isprovided with an exhaust gas discharging assembly at a downstream sidethereof for discharging of the exhaust gas from the off-road engine. Theexhaust gas discharging assembly is provided with an oxidation catalystfor converting hydrocarbon and carbon monoxide. The method comprisesinjecting a fuel rich fuel-and-air mixture into the off-road engine, andinjecting fresh air into the exhaust gas discharging assembly at anupstream side of the oxidation catalyst.

According to another aspect this invention, there is provided anemission control system for controlling emission from a four-strokeoff-road engine. The emission control system comprises: a carburetoradjusted to an operating state so as to be capable of providing a fuelrich fuel-and-air mixture to be injected into the off-road engine; amuffler adapted to be connected to the off-road engine and provided withan oxidation catalyst therein for converting hydrocarbon and carbonmonoxide in exhaust gas from the off-road engine; and an air injectionmember connected to the muffler for injecting intermittently fresh airinto the muffler at an upstream side of the oxidation catalyst by virtueof suction and compression strokes of the off-road engine.

BRIEF DESCRIPTION OF THE DRAWING

Other features and advantages of the present invention will becomeapparent in the following detailed description of the preferredembodiments of this invention, with reference to the accompanyingdrawings, in which:

FIG. 1 is a schematic diagram of the first preferred embodiment of anemission control system for an off-road engine according to thisinvention;

FIG. 2 is a schematic view to illustrate how fresh air is injected intoa muffler of the first preferred embodiment using a one-way valve; and

FIG. 3 is a schematic view to illustrate the second preferred embodimentof the emission control system according to this invention, whichemploys a one-way fan instead for injecting fresh air into the muffler.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before the present invention is described in greater detail withreference to the accompanying preferred embodiments, it should be notedherein that like elements are denoted by the same reference numeralsthroughout the disclosure.

The present invention relates to a method and an emission control systemfor controlling emission from a gasoline off-road engine, particularlyfrom a four-stroke engine with a power output of less than 30KW. Theoff-road engine is provided with an exhaust gas discharging assembly ata downstream side thereof for discharging of the exhaust gas from theoff-road engine. The exhaust gas discharging assembly is provided withan oxidation catalyst for converting hydrocarbon and carbon monoxideinto water and carbon dioxide. In order to achieve the emission control,the method of this invention includes the steps of injecting a fuel richfuel-and-air mixture into the off-road engine, and injecting fresh airinto the exhaust gas discharging assembly at an upstream side of theoxidation catalyst so as to provide sufficient oxygen for reaction withhydrocarbon and carbon monoxide in the exhaust gas upon passing throughthe oxidation catalyst.

FIGS. 1 and 2 illustrate the first preferred embodiment of an emissioncontrol system according to this invention for realizing the method ofcontrolling emission from the gasoline off-road engine.

The emission control system includes: a carburetor 10 operable to blendan air stream 101 and a fuel stream 102 and adjusted to an operatingstate so as to be capable of providing a fuel rich fuel-and-air mixture103 to be injected into the off-road engine 20; a muffler 30 of theexhaust gas discharging assembly connected to the off-road engine 20 andprovided with an oxidation catalyst 40 therein for convertinghydrocarbon and carbon monoxide in an exhaust gas stream 104 from theoff-road engine 20; and an air injection member 50 connected to themuffler 30 for injecting intermittently fresh air 105 into the muffler30 at an upstream side of the oxidation catalyst 40, which is installedin a middle of the muffler 30, by virtue of suction and compressionstrokes of the off-road engine 20. The discharged exhaust gas 106 thustreated from the muffler 30 can meet the emission standards, such asCARB III and EPA III, set in the United States.

In this embodiment, the air injection member 50 for injecting fresh air105 into the muffler 30 of the exhaust gas discharging assembly includesa reed-type one-way valve 501 (see FIG. 2) mounted on the muffler 30 andoperable in such a manner that the one-way valve 501 is opened during asuction stroke of the off-road engine 20 and is closed during acompression stroke of the off-road engine 20.

FIG. 3 illustrates the second preferred embodiment of the exhaust gasdischarging assembly of the emission control system according to thisinvention. The second preferred embodiment differs from the firstpreferred embodiment in that the air injection member 50 includes aone-way fan 502 which is operable in such a manner that the one-way fan502 is driven to rotate during a suction stroke of the off-road engine20 and is stopped from rotating during a compression stroke of theoff-road engine 20, thereby permitting intermittent injection of freshair into the muffler 30 of the exhaust gas discharging assembly.

The emission control system of this invention is advantageous in thatunder a fuel rich condition, the concentration of generated NO, in theexhaust gas is considerably reduced, which permits omission of thereduction catalyst as required in the prior art. Although theconcentration of the hydrocarbon and carbon monoxide in the exhaust gasis increased as a result of operating under a fuel rich condition, theinjection of fresh air into the muffler 30 is capable of reducing theconcentration of the hydrocarbon and carbon monoxide to an extent tomeet the aforesaid emission standards.

Table 1 shows the results of emission analysis for the off-road engine20 incorporated with or without the air injection member 50 of thisinvention and for different catalyst combinations, which arerespectively Examples 1 to 3 (represented by E. 1 to 3) and ComparativeExamples 1 to 3 (represented by CE. 1 to 3).

TABLE 1 Catalyst combination Without the air injection With the airinjection Pt/Pd/Rh member member 0/1/0 CE. 1 Emission CO 377 E. 1Emission CO 347 (g/kw-h) HC 7.1 (g/kw-h) HC 5.6 NO_(x) 2.7 NO_(x) 1.40/10/1 CE. 2 Emission CO 269 E. 2 Emission CO 244 (g/kw-h) HC 6.1(g/kw-h) HC 5 NO_(x) 3.3 NO_(x) 2.6 2/1/0 CE. 3 Emission CO 302 E. 3Emission CO 266 (g/kw-h) HC 6.2 (g/kw-h) HC 4 NO_(x) 2.3 NO_(x) 1.7

The results show that with the inclusion of the air injection member 50in the emission control system of this invention, i.e., with theinclusion of injecting fresh air into the exhaust gas dischargingassembly according to the method of this invention, the concentration ofhydrocarbon and carbon monoxide in the exhaust gas can be reducedsignificantly as compared to that without the air injection member 50 orinjection of fresh air into the muffler 30. In addition, the cost ofincorporating the air injection member 50 into the exhaust gasdischarging assembly is much cheaper than that of incorporating with theEFI means.

While the present invention has been described in connection with whatare considered the most practical and preferred embodiments, it isunderstood that this invention is not limited to the disclosedembodiments but is intended to cover various arrangements includedwithin the spirit and scope of the broadest interpretation andequivalent arrangements.

1. A method for controlling emission from a four-stroke off-road engine, the off-road engine being provided with an exhaust gas discharging assembly at a downstream side thereof for discharging of the exhaust gas from the off-road engine, the exhaust gas discharging assembly being provided with an oxidation catalyst for converting hydrocarbon and carbon monoxide, the method comprising: injecting a fuel rich fuel-and-air mixture into the off-road engine; and injecting fresh air into the exhaust gas discharging assembly at an upstream side of the oxidation catalyst.
 2. The method of claim 1, wherein injection of fresh air into the exhaust gas discharging assembly is conducted using a one-way valve which is connected to the exhaust gas discharging assembly at the upstream side of the oxidation catalyst and which is operable in such a manner that the one-way valve is opened during a suction stroke of the off-road engine and is closed during a compression stroke of the off-road engine, thereby permitting intermittent injection of fresh air into the exhaust gas discharging assembly.
 3. The method of claim 1, wherein injection of fresh air into the exhaust gas discharging assembly is conducted using a one-way fan which is connected to the exhaust gas discharging assembly at the upstream side of the oxidation catalyst and which is operable in such a manner that the one-way fan is driven to rotate during a suction stroke of the off-road engine and is stopped from rotating during a compression stroke of the off-road engine, thereby permitting intermittent injection of fresh air into the exhaust gas discharging assembly.
 4. The method of claim 1, wherein the ratio of air to fuel of the fuel rich fuel-and-air mixture is adjusted using a carburetor which is disposed at an upstream side of the off-road engine.
 5. The method of claim 1, wherein the oxidation catalyst is installed in a muffler of the exhaust gas discharging assembly, and the fresh air is injected into the muffler.
 6. An emission control system for controlling emission from an off-road engine, comprising: a carburetor adjusted to an operating state so as to be capable of providing a fuel rich fuel-and-air mixture to be injected into the off-road engine; a muffler adapted to be connected to the off-road engine and provided with an oxidation catalyst therein for converting hydrocarbon and carbon monoxide in exhaust gas from the off-road engine; and an air injection member connected to said muffler for injecting intermittently fresh air into said muffler at an upstream side of said oxidation catalyst by virtue of suction and compression strokes of the off-road engine.
 7. The emission control system of claim 6, wherein said air injection member includes a one-way valve connected to said muffler.
 8. The emission control system of claim 6, wherein said air injection member includes a one-way fan connected to said muffler. 